High field open MRI magnet isolation system and method

ABSTRACT

A vertically-aligned open MRI magnet system includes first and second (i.e., top and bottom) assemblies each having a longitudinally-extending and vertically-aligned axis, a superconductive main coil, and a vacuum enclosure enclosing the main coil. At least one support beam has a first end attached to the first assembly and has a second end attached to the second assembly. A vibration isolation system supports the magnet system.

BACKGROUND OF INVENTION

[0001] The present invention relates generally to a magnetic resonanceimaging (MRI) system, and more particularly to an open MRI magnet systemhaving a vibration isolation system.

[0002] MRI magnets include resistive and superconductive MRI magnetsused in various applications, such as medical diagnostics. Knownsuperconductive MRI magnets include liquid-helium-cooled,cryocooler-cooled, and hybrid-cooled superconductive magnets. Typically,the superconductive coil assembly includes a superconductive main coilsurrounded by a thermal shield surrounded by a vacuum enclosure. Acryocooler-cooled MRI magnet typically also includes a cryocoolercoldhead externally mounted to the vacuum enclosure, having its firststage in solid conduction thermal contact with the thermal shield, andhaving its second stage in solid conduction thermal contact with thesuperconductive main coil. A liquid-helium-cooled MRI magnet typicallyalso includes a liquid-helium vessel surrounding the superconductivemain coil with the thermal shield surrounding the liquid-helium vessel.A hybrid-cooled MRI magnet uses both liquid helium (or other liquid orgaseous cryogen) and a cryocooler coldhead, and includes designs whereinthe first stage of the cryocooler coldhead is in solid conductionthermal contact with the thermal shield and wherein the second stage ofthe cryocooler coldhead penetrates the liquid-helium vessel torecondense “boiled-off” helium.

[0003] Known resistive and superconductive MRI magnet designs includeclosed MRI magnets and open MRI magnets. Closed MRI magnets typicallyhave a single, tubular-shaped resistive or superconductive coil assemblyhaving a bore. The coil assembly includes several radially-aligned andlongitudinally spaced-apart resistive or superconductive main coils eachcarrying a large, identical electric current in the same direction. Themain coils are thus designed to create a magnetic field of highuniformity within a typically spherical imaging volume centered withinthe MRI magnet's bore where the object to be imaged is placed.

[0004] Open MRI magnets, including “C” shape and support-post MRImagnets, typically employ two spaced-apart coil assemblies with thespace between the assemblies containing the imaging volume and allowingfor access by medical personnel for surgery or other medical proceduresduring magnetic resonance imaging. The patient may be positioned in thatspace or also in the bore of the toroidal-shaped coil assemblies. Theopen space helps the patient overcome any feelings of claustrophobiathat may be experienced in a closed MRI magnet design.

[0005] It is also known in open MRI magnet designs to place an iron polepiece in the bore of a resistive or superconductive coil assembly. Theiron pole piece enhances the strength of the magnetic field and, byshaping the surface of the pole piece, magnetically shims the magnetimproving the homogeneity of the magnetic field. Nonmagnetizable supportposts are connected to the face of the pole pieces. It is additionallyknown in horizontally-aligned open MRI magnets to support the magnet onthe floor using two spaced-apart feet attached to each assembly, suchfeet raising the assemblies to provide room underneath the assembliesfor necessary wires, pipes, etc.

[0006] The sharpness of an MRI image depends, in part, on the magneticfield in the imaging volume being time-constant and highly uniform.However, the magnetic field in prior art systems suffers time andspatial deformation caused by vibrations from environmentaldisturbances. Minor relative motions between any of the magneticelements will cause significant magnetic field disturbances, thusreducing the image quality.

SUMMARY OF INVENTION

[0007] In accordance with one preferred aspect of the present invention,there is an open MRI system, comprising an open MRI magnet system, and avibration isolation system adapted to support the MRI magnet system.

[0008] In accordance with another preferred aspect of the presentinvention, there is provided an open MRI system comprising a first and asecond assembly. Each assembly comprises a longitudinally-extending andgenerally-vertically-aligned axis, at least one superconductive maincoil positioned around the axis and carrying a main electric current ina first direction, and a vacuum enclosure enclosing said at least onesuperconductive main coil. The system further comprises at least onesupport beam external to the vacuum enclosures, having a first endattached to said first assembly and having a second end attached to saidsecond assembly. The system further comprises a vibration isolationsystem.

[0009] In accordance with another preferred aspect of the presentinvention, there is provided a method of installing an open MRI system,comprising measuring environmental disturbances and vibrations at afirst site, and providing the open MRI system which comprises avibration isolation system and an open magnet system. The method furthercomprises selecting the vibration isolation system based on themeasuring step, and installing the MRI system at the first site.

[0010] In accordance with another preferred aspect of the presentinvention, there is provided a method of retrofitting a preexisting openMRI system comprising attaching a vibration isolation system to themagnet system of the preexisting MRI system.

BRIEF DESCRIPTION OF DRAWINGS

[0011] FIGS. 1-6 are schematic side cross sectional views of portions ofan MRI system according to the preferred embodiments of the presentinvention. In the drawings, the same numerals represent the sameelements throughout.

DETAILED DESCRIPTION

[0012] The present inventors have realized that all sites containing anMRI system are subject to some kind of environmental disturbance, suchas from electrical or mechanical equipment installed within the samebuilding. The environmental disturbances or vibrations excite the MRIsystem magnets through the MRI system's attachment to the building, suchas through the floor, walls or ceiling of a room of a buildingcontaining the MRI system. The most significant such attachment is thefoot support, which is fastened to the floor to secure the magnets ofthe MRI system. The foot support transmits the environmentaldisturbances and vibrations to the magnets of the MRI system, thusdegrading the image quality.

[0013] The present inventors have determined that by using a tunablevibration isolation system instead of conventional feet or other rigidsupport structures found on horizontally-aligned open MRI magnets,allows the natural frequency of the MRI magnets to be shifted to a sitedefined value. This allows the natural frequency of the MRI magnets tobe set at a value at which the sensitivity of the magnets to vibrationat the dominant frequencies imparted to the magnets by environmentaldisturbances is reduced or minimized. If desired, an optional adjustablebalance mass may be used in combination with the vibration isolationsystem to improve the gravity stability of the vibration isolationsystem when pneumatic isolators are used.

[0014] The vibration isolation system is particularly advantageous whenused with in a vertically-aligned open MRI magnet system arranged in a“clam-shell” configuration. The superconductive coils of the magnetassemblies of such MRI systems are especially subject to vibrations fromthe environment because the magnet assemblies are attached by only twosupport members, especially when the two support members are notdiametrically aligned to the diameter line of the magnet assemblies.Such clam-shell support is a very open support, providing ease ofpatient table access to the imaging volume and providing ease of patientpositioning within the imaging volume. Engineering analysis shows thatthe vibration isolation system reduces magnet vibrations in avertically-aligned open MRI magnet having a “clam-shell” configuration.However, the isolation system may be used for MRI systems having aconfiguration other than a “clam-shell” configuration, if desired.

[0015] The vibration isolation system is also advantageous because it isfairly inexpensive. The isolation system may utilize commerciallyavailable isolators which are configured to support a new MRI magnetsystem or retrofitted to an preexisting MRI magnet system.

[0016]FIG. 1 conceptually shows components of an isolation system for anMRI system 1 arranged in a “clam-shell” configuration according to apreferred aspect of the present invention. The isolation system is madeup of a vibration isolation system 2 and an optional, adjustable balancemass 3. The vibration isolation system 2 includes a conceptual variablespring element 4 and a conceptual variable damper element S. The springelement 4 and the damping element 5 may integrated into the same deviceor they may comprise different devices (i.e., in this case, the system 2comprises two discrete devices). It should be noted that any or all ofthese conceptual elements 3, 4 and 5 should be broadly construed andinclude many elements which have similar performance characteristics.For example, the spring element 4 includes mechanical springs, airisolators, piezoelectric actuator isolators, elastic webbing or otherdevices which provide frequency isolation.

[0017]FIG. 2 illustrates a portion of an MRI system according to thefirst embodiment of the present invention. The MRI system includes anopen MRI magnet system 10, which contains a first magnet assembly 12, asecond magnet assembly 14 and at least one support member (such as thetwo support beams 1 6 and 18 that are shown in FIG. 2), and a vibrationisolation system 20. However, more than two support beams or other typesof support members (i.e., “C” shaped supports) may be provided.Additional parts of the MRI system, such as the control electronics andcooling fluid supply pipes, are not shown in FIG. 2 for clarity.

[0018] The first assembly 12 has a longitudinally-extending andgenerally-vertically-aligned first axis 22, at least one superconductivemain coil 24, and a first vacuum enclosure 26. By“generally-vertically-aligned” is meant vertically aligned plus or minustwenty degrees. The at least one superconductive main coil 24 of thefirst assembly 1 2 is generally coaxially aligned with the first axis 22and carries a first main electric current in a first direction. Thefirst direction is defined to be either a clockwise or acounterclockwise circumferential direction about the first axis 22 withany slight longitudinal component of current direction being ignored.The first vacuum enclosure 26 encloses at least one superconductive maincoil 24 of the first assembly 12 and preferably surrounds a first bore70. A first magnet pole piece 68 is generally coaxially aligned with thefirst axis 22, is disposed inside the first bore 70 and outside thefirst vacuum enclosure 26, and is attached to the first vacuum enclosure26.

[0019] The second assembly 14 is longitudinally spaced apart from anddisposed generally vertically below the first assembly 12. The secondassembly 14 has a longitudinally-extending second axis 28, at least onesuperconductive main coil 30, and a second vacuum enclosure 32. Thesecond axis 28 is generally coaxially aligned with the first axis 22. Atleast one superconductive main coil 30 of the second assembly 14 isgenerally coaxially aligned with the second axis 28 and carries a secondmain electric current in the previously-described first direction. Thesecond vacuum enclosure 32 encloses the at least one superconductivemain coil 30 of the second assembly 14 and preferably surrounds a secondbore 74. A second magnet pole piece 72 is generally coaxially alignedwith the second axis 28, is disposed inside the second bore 74 andoutside the second vacuum enclosure 32, and is attached to the secondvacuum enclosure 32. The vacuum enclosure 32 contains generallyhorizontally-aligned annular shaped walls 60 and 62 andcircumferentially-extending walls 64 and 66. Walls 60, 62, 64 and 66enclose the coil 30.

[0020] At least one support member, such as the support beams 16 and 18,has a first end 34 attached to the first assembly 1 2 and has a secondend 36 attached to the second assembly 14. Each support beam or memberis preferably made of a nonmagnetizable material or includes at least anonmagnetizable material portion which blocks having a magnetizable pathbetween its ends. Such nonmagnetizable material has a relativepermeability of generally unity. Examples of nonmagnetizable materialsinclude aluminum, copper, nonmagnetic stainless steel, plastic, wood,etc.

[0021] The vibration isolation system 20 of the embodiment of FIG. 2contains of one or more isolators 1 20 positioned beneath the second(i.e., lower) assembly 14. In this embodiment, the isolators 120 can beeither passive or active isolators. For example, passive pneumaticisolators, such as Gimbal Piston or MaxDamp®, or active isolators, suchas STACIS® 2000 or 3000 Active Piezoelectric Vibration Control Systemunits may be used. These isolators are made by Technical ManufacturingCorporation (TMC) in Peabody, Mass. (see www.techmfg.com).

[0022] The pneumatic isolators work by the pressure in a volume actingon an area of a piston to support the load against the force of gravity.A reinforced rolling rubber diaphragm forms a seal between the air tankand the piston. The pressure in the isolator is controlled by a heightcontrol valve which senses the height of the payload, and inflates theisolator until the payload is “floating.” Thus, in this case, theisolator assembly 120 acts as a spring element and as a damper.

[0023] In the active isolators 120, actively controlled piezoelectricactuators are used to cancel the vibration on the payload (i.e., the MRImagnet system). This system contains an “inner-loop” damping function,in which vibration sensors measure floor noise, which is conditioned andused to cancel vibration, and an “outer-loop” damping function, in whichvibration sensors mounted on payload side of the system measure theresidual vibration on the payload, which is used in a feed back loop tofurther reduce vibration. It should be noted that any other commercialoff the shelf or custom build isolator can be used instead, providingthat it provides the appropriate vibration isolation.

[0024] In the embodiment of FIG. 2, the isolators 120 provide the onlyweight-bearing support for the second assembly 14 (and preferably forthe entire magnet system 10). The isolators 120 are positioned withrespect to the second axis 28 in such a manner that each isolator bearsa desired load. For example, four to twenty, preferably ten isolators120 may be arranged within the footprint of the second assembly 14 tosupport the magnet system 10. The isolators 120 are attached to a floor42 of a building or other support for the MRI system.

[0025] In an alternative aspect of the present invention, the vibrationisolation system 20 comprises a material which is capable of isolatingvibration from the environment. This material, acts as a spring elementand as a damper. For example, the vibration isolation system 20 maycomprise a rubber mat or rubber blocks placed between the magnet system10 and the floor 42.

[0026] The isolation system 20 may be exposed (i.e., visible below themagnet system 10) or it may be enclosed. Preferably, the isolationsystem 20 is enclosed by an enclosure (not shown in FIG. 2 for clarity)for aesthetic, sanitary, acoustical reasons. It is desirable to have theisolation system 20 contained within the footprint of the MRI magnetsystem 10, whether it is enclosed or not enclosed.

[0027] Preferably, the vibration isolation system 20 provides anadjustable damping and spring constant. This allows the adjustment ofthe natural frequency of the MRI magnet system 10 to a site definedregion. This can be done both at the manufacturer's facility and at theMRI system installation site. The isolation system 20 is preferablyselected such that its damping function minimizes the magnet system Qfactor and controls the bandwidth of the vibrational response at thepredominant exciting frequencies. Furthermore, the isolation system alsopreferably provides a sufficiently high damping to improve thegravitational stability of the magnet system. Thus, the isolators 120are selected such that they can provide the above functions.

[0028] In a second preferred embodiment, the vibration isolation system20 is used in a retrofit of a preexisting (i.e., a prior art) MRIsystem, as shown in FIG. 3. A prior art MRI system is ordinarily rigidlyattached (i.e., bolted, clamped and/or welded) to a floor of a buildingby support structure, such as by legs or by a curved skirt 124, asdescribed in U.S. Pat. No. 6,198,371, incorporated herein by reference.In retrofitting the MRI system, in order to decrease the retrofittingcosts, after the MRI system is detached from the floor (i.e., unbolted,unclamped, etc), the support legs or skirt 124 are not removed from theMRI system. Thus, instead of removing the existing supports, thevibration isolation system 20 can be colocated with the supports. Allthat is necessary is to raise the height of the MRI magnet assembly 10so that the bottom of the preexisting support structure does not contactthe floor 42 of the building. As shown in FIG. 3, posts 122 or otherload bearing objects are placed under the isolators 120 to elevate theMRI magnet assembly 10 to a height sufficient to prevent the supportlegs or skirt from contacting the building floor 42.

[0029] In a third preferred embodiment of the present invention, anoptional structural holder 126 is located between the isolators 120 andthe lower assembly 14 of the magnet system 10, as shown in FIG. 4. Theholder 126 may be one or more a metal or other plates which are placedbetween the isolators 120 and the lower assembly 14. The holder ispreferably lightweight, compact in size and provides a level surface forthe isolators 120. The holder 126 is advantageous when the lower surfaceof the second assembly 14 is not sufficiently level or does not have adesired shape or material to allow the isolators 120 to be connecteddirectly to the second assembly. Thus, the holder 126 may beparticularly advantageous for retrofitting a preexisting MRI system,where the second assembly 14 was not designed to be directly connectedto the isolators 120.

[0030] In a fourth preferred embodiment of the present invention, abalance mass 128 is added to the isolation system 20, as shown in FIG.5. In this embodiment, the balance mass 128 is supported by a balancemass support 130 that is connected the structural holder 126.Alternatively, the balance mass 128 can be connected directly to thestructural holder 126, or directly to the lower assembly 14 of themagnet system if the holder 126 is omitted. The balance mass 128 may beany heavy object, such as metal or ceramic bars or weights. Preferably,the optional posts 122 are also used in combination with the balancemass 128 to raise the isolators off the floor 42 to provide sufficientclearance for the placement of the balance mass, as shown in FIG. 5.

[0031] The balance mass 128 is preferably adjustable to allow the centerof gravity of the magnet assembly 10 to be changed to improvegravitational stability. The balance mass 128 may be adjusted by raisingor lowering it with respect to the magnet system 10. The adjustments maybe made, for example, by manually (i.e., by using a jackscrew or similarelements), electrically or hydraulically raising or lowering the support130. Alternatively, the adjustments may be made by adding or removingmass from the balance mass 128. For example, one or more weightproviding plates may be added or removed from the balance mass foradjustment. Most preferably, the balance mass 128 is adjustable on site(i.e., in the building that will house the MRI system), after theenvironmental vibrations at this site have been determined.

[0032] A structure supported below its center of mass is inherentlyunstable because as the structure tilts, its center of mass moveshorizontally in a way that wants to further increase the tilt. Themaximum allowed height of the magnet system center of mass improves withthe square of the isolator 120 separation, and the stiffness of theisolators 120. The balance mass 128 lowers the center of mass of thestructure to improve the gravitational stability of the structure.Supporting the magnet system 10 closer to its center of mass will reducethe rocking of the magnet system 10 and thus improve the MRI image. Thebalance mass 128 can be configured in such a way as to work with theisolators to change the system natural frequency and reduce themagnitude of the vibrations experienced by the magnet system 10.

[0033] The fifth embodiment of the present invention is illustrated inFIG. 6, where the balance mass 128 is used with pneumatic (i.e., air)isolators 120. The isolators 120 are supplied with air (or another gas)from an air source 132 through a line 134. A height control valve 136 isalso provided to control the flow of air through the line 134 to controlthe pressure in the isolators 120. The valve 136 may be manually orcomputer controlled. FIG. 6 also shows an alternative configuration ofthe isolation system 20, where the optional balance mass 128 isconnected directly to the structural holder 126, and the balance masssupport is omitted.

[0034] The MRI system may be installed at a particular site as follows.The environmental disturbances and vibrations at a particular site aremeasured. The measurements are preferably made before the MRI system isinstalled at a particular site.

[0035] Then, based on the measurements, the isolators are selected suchthat the natural frequency of the MRI magnet system and the damping ofthe isolators will provide significant reduction on ground vibrationtransmissibility over the entire frequency band. A high damping isolatorsystem is preferably selected when low frequency excitation (i.e.,vibrations or disturbances) is significant at the particular site. A lowdamping isolator system is preferably selected if the particular sitehas only high frequency disturbances or vibrations.

[0036] Furthermore, the damping of the isolators is adjusted to minimizethe magnet system Q factor and control the bandwidth of the vibrationalresponse of the magnet system at the predominant exciting frequencies.If a balance mass 128 is present, then the balance mass is adjusted tooptimize the center of gravity of the system and the natural frequencyof the MRI magnets. Thus, the frequency and damping are site tunablebecause they are adjusted to be optimized for a particular site. Theadjustments may be made before or after the MRI system has beeninstalled at a particular site (i.e., attached to a floor 42 of thebuilding that houses the MRI system).

[0037] It should be noted that additional gradient coils,superconductive main coils, superconductive shielding coils,superconductive correction coils, and magnetizable rings may be present,as is known to the artisan, but such coils and rings have been omittedfrom the figures for clarity. Likewise, coil forms (if needed) tosupport the superconductive main coils and spacers to position a thermalshield with respect to a cryogenic vessel and to position a thermalshield with respect to a vacuum enclosure have been omitted from thefigures for clarity but are well known to those skilled in the art.

[0038] The preferred embodiments have been set forth herein for thepurpose of illustration. However, this description should not be deemedto be a limitation on the scope of the invention. Accordingly, variousmodifications, adaptations, and alternatives may occur to one skilled inthe art without departing from the scope of the claimed inventiveconcept.

1. An open MRI system comprising: an open MRI magnet system; and avibration isolation system adapted to support the MRI magnet system. 2.The open MRI system of claim 1, wherein a spring constant and damping ofthe vibration isolation system are adjustable.
 3. The open MRI system ofclaim 1, wherein the vibration isolation system comprises a plurality ofpneumatic isolators.
 4. The open MRI system of claim 1, wherein thevibration isolation system comprises a plurality of active vibrationcontrol isolators.
 5. The open MRI system of claim 1, further comprisinga balance mass.
 6. The open MRI system of claim 5, wherein the balancemass is adjustable.
 7. The open MRI system of claim 1, wherein thevibration isolation system is secured to a floor and the MRI magnetsystem is attached over the vibration isolation system.
 8. The open MRIsystem of claim 1, wherein the vibration isolation system is configuredwithin a footprint of the MRI magnet system.
 9. The open MRI system ofclaim 1, further comprising a structural holder positioned between thevibration isolation system and the MRI magnet system.
 10. The open MRIsystem of claim 1, wherein the vibration isolation system is retrofittedto a preexisting MRI magnet system.
 11. The open MRI system of claim 10,wherein the vibration isolation system is mounted on posts such that MRImagnet system supports do not contact a floor of a site where the MRImagnet system is located.
 12. The open MRI system of claim 1, whereinthe vibration isolation system is site tunable.
 13. The open MRI systemof claim 11, wherein the vibration isolation system is tuned to minimizethe magnet system Q factor and to control a bandwidth of the MRI magnetsystem vibration response at a predominant MRI magnet excitingfrequencies.
 14. An open MRI system comprising: (a) a first assemblycomprising: (1) a longitudinally-extending andgenerally-vertically-aligned first axis; (2) at least onesuperconductive main coil positioned around said first axis and carryinga first main electric current in a first direction; and (3) a firstvacuum enclosure enclosing said at least one superconductive main coilof said first assembly; (b) a second assembly longitudinally spacedapart from and disposed below said first assembly, comprising: (1) alongitudinally-extending second axis generally coaxially aligned withsaid first axis; (2) at least one superconductive main coil positionedaround said second axis and carrying a second main electric current insaid first direction; and (3) a second vacuum enclosure enclosing saidat least one superconductive coil of second assembly; (c) at least onesupport beam external to said first and second vacuum enclosure having afirst end attached to said first assembly and having a second endattached to said second assembly; and (d) a vibration isolation system.15. The open MRI system of claim 14, wherein a spring constant anddamping of the vibration isolation system are adjustable.
 16. The openMRI system of claim 14, wherein the vibration isolation system comprisesa plurality of pneumatic isolators.
 17. The open MRI system of claim 14,wherein the vibration isolation system comprises a plurality of activevibration control isolators.
 18. The open MRI system of claim 1 4,further comprising an adjustable balance mass.
 19. The open MRI systemof claim 14, wherein the vibration isolation system is secured to afloor and the MRI magnet system is attached over the vibration isolationsystem.
 20. The open MRI system of claim 14, wherein the vibrationisolation system is configured within a footprint of the MRI magnetsystem.
 21. The open MRI system of claim 14, wherein: the vibrationisolation system is retrofitted to a preexisting MRI magnet system; andthe vibration isolation system is mounted on posts such that MRI magnetsystem supports do not contact a floor of a site where the MRI magnetsystem is provided.
 22. The open MRI system of claim 14, wherein thevibration isolation system is site tuned to minimize the magnet system Qfactor and to control a bandwidth of the MRI magnet system vibrationresponse at a predominant MRI magnet exciting frequencies.
 23. Themethod of installing an open MRI system, comprising: providing the openMRI system which comprises a vibration isolation system and an openmagnet system; measuring environmental disturbances and vibrations at afirst site; selecting the vibration isolation system based on themeasuring step; and installing the MRI system at the first site.
 24. Themethod of claim 23, wherein the step of selecting comprises: selecting ahigh damping isolation system when significant low frequency vibrationsor disturbances are measured at the first site; or selecting a lowdamping isolation system when only high frequency disturbances orvibrations are measured at the first site.
 25. The method of claim 24,further comprising adjusting a balance mass to optimize a center ofgravity of the magnet system.
 26. The method of claim 25, wherein thestep of adjusting is performed before or after the step of installing.27. The method of claim 23, wherein the step of measuring is performedbefore the step of installing.
 28. The method of claim 23, wherein thesteps of measuring and selecting are performed before the step ofinstalling.
 29. The method of claim 23, further comprising adjusting thedamping of the vibration isolation system to minimize the magnet systemQ factor and control a bandwidth of a vibrational response atpredominant exciting frequencies.
 30. The method of claim 23, whereinthe vibration isolation system comprises a plurality of pneumaticisolators.
 31. The method of claim 23, wherein the vibration isolationsystem comprises a plurality of active vibration control isolators. 32.The method of claim 23, wherein the step of installing comprisessecuring the vibration isolation system to a floor, such that the MRImagnet system is provided over the vibration isolation system.
 33. Themethod of claim 23, further comprising: detaching the MRI system from afloor; and retrofitting the vibration isolation system to the magnetsystem of the MRI system prior to the step of installing the MRI systemat the first site.
 34. A method of retrofitting a preexisting open MRIsystem comprising attaching a vibration isolation system to a magnetsystem of the preexisting MRI system.
 35. The method of claim 34,further comprising detaching the magnet system from a floor prior to thestep of attaching the a vibration isolation system.
 36. The method ofclaim 34, wherein the vibration isolation system comprises a pluralityof pneumatic isolators.
 37. The method of claim 34, wherein thevibration isolation system comprises a plurality of active vibrationcontrol isolators.
 38. The method of claim 34, further comprisingsecuring a plurality of posts to a floor and securing the vibrationisolation system to the posts, such that the MRI magnet system isprovided over the vibration isolation system and such that supports ofthe preexisting MRI system do not contact the floor.